DE102012005654B4 - Optical converter for high luminance levels - Google Patents

Abstract

Converter arrangement for generating colored or white useful light of high luminance for projectors, stage headlights, car headlights or lamps with high luminance and high spectral density, whereby the most complete possible decoupling of the converted light is to be achieved with a spatially small emission spot, comprising: - a converter body (1) with an excitation side and a side facing away, containing an optoceramic with YAG ceramic or LuAG ceramic with embedded grain structure for purposes of strong light scattering, - an excitation light source with a light beam cross-section that determines the spatially small emission spot to be reached, the excitation light source for irradiating the Converter body (1) is arranged with blue excitation light of high power density, which generates a blue light scattering spot and secondarily the emission spot which is larger than the light beam cross-section of the excitation light source, - the thickness of the Ko Inverter body (1) is chosen sufficiently thin between the excitation side and the opposite side, on the one hand to minimize an expansion of the light scattering spot and on the other hand to effect a sufficient conversion of the blue excitation light with regard to the color of the useful light.

Description

The invention relates to an optical converter for generating colored or white useful light of high luminance for projectors, stage headlights, car headlights or lamps with high luminance and high spectral density, whereby the most complete possible decoupling of the converted light with a spatially small emission spot is to be achieved.

The shorter-wave excitation light is converted into remitted light with a longer wavelength by absorption and emission processes in the converter material.

In the context of the invention, a converter is understood to mean that part of a device for optical conversion in which the conversion takes place. The converter consists of a converter material. Converter materials contain phosphors which, as optically active media, cause the conversion. Converter materials can have different high phosphor densities. The term “phosphor density” refers to the distribution of the phosphor or the phosphor particles in the converter material. The phosphor can be present in the converter material in a passive matrix. However, converter materials are also possible in which the entire converter material functions as a phosphor.

In the case of optical conversion, the so-called Stokes losses always generate heat in the converter. The Stokes losses result from the difference in the photon energy of the excitation light and the emitted light. Typically 20-30% of the introduced optical power is converted into heat. This applies even to converter materials with a quantum efficiency of 1. The heat input into the converter leads to an increase in the temperature of the converter material.

For several reasons, the high temperatures in the converter material lead to a weakening or limitation of the conversion and thus to a limitation of the luminance that can be achieved. The converter material can be destroyed by the high temperatures. The destruction temperature T _fail is a material-specific property. Different materials can therefore have different destruction temperatures. _{The destruction} temperature has a decisive influence on the maximum converter temperature T conv, ie the maximum temperature at which the converter can be operated.

This has a limiting effect on the luminance to be achieved, in particular in the case of converter systems in which the phosphor is embedded in a matrix made of silicone or another organic binder. In the case of so-called “phosphor-in-silicon” converters, PIS, the damage threshold is T _fai | in the range from 100 to 120 ° C.

Regardless of the destruction threshold of the converter materials used, the quantum efficiency is reduced by the effect of thermal quenching. In addition, at higher temperatures there can be a shift in the absorption band to longer wavelengths, which leads to an increase in self-absorption and thus also to a reduction in luminance.

In order to still obtain converters with high luminance densities, structures in which the converter material is located on a rotating disk are known from the prior art. So describes the patent application US 2009/0073591 A1 a converter with a converter material applied to a rotating carrier wheel. Due to the dynamic design, the heat output can be distributed over a larger area and the temperature limit can be adhered to.

A similar structure is also described in patent application US 2009/0 034 284 A1. The disadvantage of this approach, however, is the absolutely necessary use of a carrier wheel and its disadvantageous influence on the size of the converter. In addition, the large carrier wheels require more material than, for example, a static structure. In addition, the moving components can cause disruptive noise development or wear out.

Therefore, WO 2009/115 976 A1 A provides for the use of a heat sink. The converter material is statically applied to a heat sink. This design is limited to converters operated in remission. In addition, the heat dissipation to be achieved depends on the thermal conductivity of the converter material used.

Out US 2010/0067233 A1 a converter arrangement for emitting mixed light is known, in which a layer structure of light sources emitting areally and a directly adjacent light converting element is encountered, which is laterally bounded by mirror surfaces and is arranged within a lens space. The mixed light of primary and secondary radiation is essentially independent of the viewing angle, that is, it radiates uniformly into a usable space.

WO 2009/094994 A1 relates to an opto-electronic module and a projection device with this opto-electronic module, which emits monochromatic radiation in the visible wavelength range and for this purpose has blocking filters for the UV excitation light on the flat light-emitting side.

Out WO 2010/010484 A1 shows a light-emitting device with a converter layer made of sintered ceramic with a light-scattering layer made of porous material connected to this and with a light-emitting diode.

The US 2005/0269582 A1 describes a semiconductor light-emitting device in combination with a converter as a ceramic layer.

Usually, materials based on phosphors, for example embedded in silicone or glass or quantum dots, are used as converter materials. In particular, converter materials based on silicone show low destruction temperatures of approx. 100-120 ° C and low thermal conductivities. In addition, when using phosphor particles in a matrix, the difference in refractive index can only be varied to a limited extent via the doping and grain size of the phosphor particles. As a result, the absorption of the excitation light and the scattering in the converter body cannot be set independently of one another.

The scattering properties of the converter material influence both the scattering of the converted light and the scattering of the excitation light and are therefore an important optical parameter.

For the generation of high luminance densities, as complete a coupling out of the converted light as possible with a spatially small emission spot is advantageous. The emission spot is determined by the light beam cross section of the excitation light and the luminance by the emitted luminous flux per surface element of the converter surface. Because of the finite penetration depth of the excitation light and because of the light scattering in the converter material, the emission spot is larger than the light beam cross-section of the excitation light source. The emission spot is smaller with strongly scattering converter material than with weakly scattering converter material, but it also depends on the converter thickness and the reflection properties of the converter surface.

A high luminance can be achieved through highly scattering material. However, if the material scatters so strongly that the excitation light is also reflected before it is absorbed, the proportion of the converted light decreases.

The invention is based on the object of providing a converter for generating white or colored light with high luminance.

The object of the invention is achieved by the subject matter of the independent claim and is designed and developed by the features of the dependent claims.

The converter according to the invention consists of a doped YAG ceramic or LuAG ceramic, which represent an optoceramic with an embedded grain structure which form conversion centers directly in the ceramic material. YAG ceramic is a yttrium aluminum garnet and LuAG ceramic is a lutetium aluminum garnet. Doping with a cerium compound, for example Ce ₂ O _3, is particularly advantageous.

By using the optoceramics according to the invention as converter material, high luminance densities, preferably of over 100 cd / mm ² , particularly preferably of over 500 cd / mm ² , can be achieved.

For the generation of high luminance densities, as complete a coupling out of the converted light as possible with a spatially small emission spot at the same time is advantageous. This can be achieved with a highly scattering converter material. The grain structure according to the invention leads to good scattering of both the short-wave excitation light and the long-wave emission light. A strong scattering of the emission light generated in the converter is particularly advantageous for achieving a good light confinement, i.e. for a small emission spot.

However, if the excitation light is remitted by the converter, the proportion of the excitation light that penetrates the converter and can contribute to the conversion there decreases. Therefore, the scattering - for a given absorption length - must again not be so strong that the remission of the excitation light exceeds a desired level. The conversion efficiency is influenced both by the absorption of the excitation light, ie the quantum efficiency, and by the remission of the excitation light.

As expected, however, the conversion efficiency would decrease in the case of strongly scattering samples, that is to say in the case of samples with a high remission R _emission . This dependency is known in the case of converter materials in which phosphor particles are present in an optically inactive matrix. In the case of converter materials, such as, for example, phosphor particles in a silicone matrix, a high phosphor particle density in the silicone matrix leads to a high remission. However, a high phosphor density causes an increase in the remission of the excitation light. In order to maintain the desired absorption of the excitation light, the phosphor must be doped more heavily. This results in what is known as concentration quenching, ie the quantum yield and thus the conversion efficiency are reduced. So far it has therefore not been possible to achieve a high conversion efficiency and a high remission R _{emission at the same time.} Surprisingly, the optical ceramic according to the invention has a high degree of scattering or remission R _emission , at which the conversion efficiency is not yet adversely affected.

In particular, the remission R _{emission is} preferably at least 60%, particularly preferably at least 80%. This is advantageous since strong scattering is required for sufficient light confinement and thus for high radiation density.

Furthermore, the converter material preferably has a quantum efficiency QE of the absorption of the excitation light greater than 80% and particularly preferably greater than 90%. This is particularly advantageous because a high quantum yield means that a smaller proportion of the radiated energy is given off in the form of heat. As a result, the good quantum efficiency of the converter material according to the invention, on the one hand, minimizes heating.

On the other hand, light sources with lower light intensity can be used, which is advantageous in terms of energy consumption.

Since both high absorption of the excitation light and high remission of the converted emitted light are required to achieve high luminance, the product of remission R _emission and quantum efficiency is in any case greater than 0.6 and preferably greater than 0.7.

According to the prior art, a ceramic material with particularly good quantum efficiency would be expected to have a low scatter (and thus a low remission R _emission ).

größer als 0.6, bevorzugt größer als 0.7 und besonders bevorzugt größer als 0.8 auf. Dabei soll die Quanteneffizienz größer als 0.8 sein. Die nach dem Stand der Technik zu erwartenden FOM_opt sind dagegen deutlich kleiner.In contrast, the converter material according to the invention has, in a highly surprising manner, a high degree of scattering (and thus a high remission R _emission ) without the quantum efficiency being adversely affected.
The converter according to the invention thus has a converter figure of merit or optical figure of merit FOM _opt , defined as $${\text{FOM}}_{\text{opt}}=\text{QE}*{\text{R.}}_{\text{emission}\text{,}}$$

greater than 0.6, preferably greater than 0.7 and particularly preferably greater than 0.8. The quantum efficiency should be greater than 0.8. _{In contrast, the FOM opt} to be expected according to the state of the art are significantly smaller.

This extraordinary and highly advantageous FOM _opt is an intrinsic feature of the converter material according to the invention.

In an advantageous development of the invention, the aim is to convert all of the excitation light as far as possible. Then the product QE * (1-R _excitation ) * R _{emission is to be selected} as the indicator for the conversion efficiency. In the advantageous development of the invention, this code number is therefore greater than 0.4, preferably greater than 0.6 and particularly preferably greater than 0.75. The high index numbers in this development of the invention are made possible by the fact that the absorption of the excitation light by the converter material can surprisingly be set largely independently of the scattering properties. So can the absorption length of the converter according to the invention can be selected so that it is smaller than the typical scattering lengths.

By using an optical ceramic according to the invention as a converter material, it is possible to adjust the scattering power of the material between highly transparent and highly opaque independently of the activator concentration by means of suitable process management.

In addition, the optical properties can also be influenced in a targeted manner via the initial composition and / or via the degree of doping. Together with the excellent thermal and thermo-optical properties of the optoceramics, converters with tailor-made properties are accessible, which enable high luminance levels.

In static operation, the converters according to the invention have high luminance levels of at least 100 cd / mm ² , preferably of at least 500 cd / mm ^2, at luminous fluxes greater than 1000 .mu.m.

zusammengefasst werden. Die thermische FOM berücksichtigt die Wärmeleitfähigkeit und die maximal zulässige Temperaturbelastung des Konvertermaterials.The thermo-optical properties of the converter material can be expressed in a thermal figure of merit, FOM, $$\begin{array}{l}{\text{FOM}}_{\text{therm}}=\text{W.}\ddot{\text{a}}\text{line code}*\left(\text{W.}\ddot{\text{a}}\text{rmekapazit}\ddot{\text{a}}\text{t / volume}\right)\\ *\text{min}\left({\text{T}}_{\text{fail}},{\text{T}}^{0.8}{}_{\text{quench}}\right)\end{array}$$

be summarized. The thermal FOM takes into account the thermal conductivity and the maximum permissible temperature load of the converter material.

The _{destruction temperature T fail} is the temperature at which the converter material is destroyed.

When the temperature is increased, thermal quenching leads to a decrease in the quantum efficiency. The limit temperature T ^0.8 _quench is defined as the temperature at which the quantum efficiency is 80% of its value at room temperature.

Converters whose converter materials have a high thermal FOM can therefore be operated at higher temperatures.

Since the maximum achievable pump output of the converter is limited by the maximum converter temperature, conclusions can be drawn about the maximum pump output from the thermal FOM.

According to an advantageous development of the invention, the converter material has a thermal FOM greater than 500 (W / mK) * (J / cm ³ K) * K, preferably greater than 800 (W / mK) * (J / cm ³ K) * K on.

The exceptionally high thermal FOM is made possible by the opto-thermal properties of the optoceramics used as converter material.

It has been found that optoceramics have high thermal conductivity, a high thermal damage threshold and a high limit temperature. Optoceramics show highly advantageous thermal conductivities, in particular the thermal conductivity is greater than 5 W / m * K, preferably greater than 8 W / m * K, and particularly preferably greater than 10 W / m * K.

The limit temperature of the corresponding optoceramics is above 200 ° C, in particular above 250 ° C. Conventional converter materials such as phosphors in silicone, on the other hand, have limit temperatures of approx. 100-120 ° C.

In the case of ceramic converters, the thermal conductivity of its crystallites dominates the thermal conductivity of the entire converter. Grain boundaries and / or pores thus influence the scattering, but not the thermal conductivity of the converter.

Thus, according to the embodiment of the invention, converter materials with thermal conductivities of at least 5 W / mK, in particular of at least 8 W / mK and very particularly of at least 10 W / m * K can be obtained.

In a preferred embodiment, the converter material is designed to be self-supporting. In the context of the invention, a self-supporting converter material is understood to be a material whose strength is sufficient to be able to dispense with a substrate as a carrier material.

This is particularly advantageous since both outer sides of the converter can thus be coated. Due to the extremely high thermal stability, this is possible even at higher temperatures.
In an advantageous development of the invention, when used in transmission, the converter material is coated on the excitation side with a dichroic filter that works as an edge filter. This is highly reflective for the spectral range of the converted light, whereas it has as little reflection as possible for the excitation light.

Use in transmission here means that the excitation light is radiated into the sample on one side and the converted light is used on the opposite side (exit side). The edge filter can be an AR filter (anti-reflection filter), which has an AR effect for the excitation light, but acts as a mirror for the converted light. Thus, the occurrence of Fresnel reflection loss and the back loss of converted light can be reduced. Another broadband AR filter can be applied to the exit side.

In a further embodiment, the converter material has an AR element on the emission side for use in remission. In particular, broadband AR coatings or AR structures such as moth's eye structures are used here, which have an AR effect both for the excitation light and for the converted light.

To maximize the luminance, the converter material of this embodiment preferably has a thickness of 0.1 to 1 mm, particularly preferably 0.2 to 0.8 mm and very particularly preferably 0.3 to 0.6 mm. The luminance is proportional to the absorption of the excitation light and inversely proportional to the size of the emission spot. Thin converters minimize the widening of the emission spot.

The converter is chosen to be thin enough to minimize widening of the stray spot. The thickness of the converter is sufficient to ensure effective absorption of the excitation light.

A further development of the invention provides for static use of the converter. This is particularly advantageous because when the converter is used statically, the use of large converter wheels is not necessary. With a small converter ring, on the one hand, the use of material is low and, on the other hand, a more compact design of the converter is possible. The post-processing effort is also lower when the converter is used statically, in particular when the converter is manufactured from a solid body.

The converter preferably has a luminance of >> 100 cd / mm ² in static operation. Static operation places high demands on the converter material, since the local exposure times of the excitation light to the material are much longer than is the case with a rotating converter wheel. In particular, the converter materials used must have high thermal conductivity in order to dissipate the heat effectively. Materials with poor thermal conductivity, on the other hand, can be thermally destroyed after only short exposure times and are not suitable for use in static converters. This applies, for example, to converter materials in which the optically active components are embedded in a passive matrix made of glass or silicone.

This problem is solved by using the optical ceramic according to the invention as a converter material. The converter material according to the invention thus has high thermal conductivities and a high thermal damage threshold. In addition, the optoceramic is preferably mounted on the substrate in such a way that it is optimally coupled to a heat sink. The optoceramic can be bonded directly to the heat sink. This design is advantageous for converters that are operated in remission.

Another design provides for a lateral connection of the heat sinks to the optoceramics. The converter is dimensioned and mounted laterally in such a way that it is optimally coupled to a heat sink without obstructing the light path of the converter. This design also enables the use of a heat sink in converters operated in transmission. The use of a self-supporting converter disk can also be advantageous, particularly when there is little thermal load.

In an advantageous development of the invention, the converter material is excited in transmission. It is therefore a rear-excited converter. Converters operated in transmission enable a simpler optical design than converters operated in remission, since the input beam path and output beam path of the converted light are not interleaved with one another and / or are partially identical. However, the intensity of the excitation beam is weakened by the transmission through the converter material. The light source used must therefore provide a sufficient luminous flux. The resulting high performance requires converter materials with high maximum destruction temperatures. Due to its advantageous thermal properties, the optical ceramic according to the invention is also suitable for use in converters that operate in transmission.

According to an advantageous development of the invention, the converter material is applied to a movable carrier.

Color wheels with conversion materials are used in new types of projectors. These color wheels can be covered with segments of materials with different emission wavelengths or designed for the emission of light of one wavelength. The color wheel is preferably made of a highly reflective metal. This supports the remission of the remaining excitation light as well as the emitted light.

The cooling effect of the rotating color wheel is limited, however, since the design of the color wheel is intended in particular to ensure remission and color multiplexing. To cool the color wheel, additional fans are therefore typically used, which generate a cooling air flow.

The movable carrier of the embodiment is preferably provided with lamellar and / or ventilation elements. This can improve the cooling of the wheel. In addition, the wheel automatically ensures an air flow. This can be done independently of the cooling of other components. In particular, the wheel is provided with the above elements in the areas that are not covered with the optoceramics. For example, the slats can be placed in the center of the wheel and / or the fan segments at the edge of the color wheel. Both elements can also be used in combination. The lamellae can in particular be designed as radial or radial, twisted lamellae. Fan blades or commercially available fans with applied optoceramic reflectors can also be used. The use of a self-ventilating carrier wheel is particularly advantageous if the converter material is not designed as a circular ring but as a circular disk. Circular disks can be used in particular when the conversion element does not have to allow a color change. Possible uses are, for example, LCD projectors, LCOS projectors or 3-chip DLP projectors. Use in hybrid versions is also possible. In hybrid devices, the generation of light via fluorescence conversion is combined with directly emitting semiconductor sources.

The use of the self-ventilating wheel is particularly advantageous in applications that do not require synchronization of the color wheel and imaging. In this case, an unsynchronized fan motor can be used. However, the construction of the self-ventilating wheel can also be used with segmented, synchronized color wheels.

In another embodiment of the invention
the remission of the excitation light is adjusted by the doping level of the optoceramics so that the excitation light is present in the remitted light spectrum.

By mixing the remission of the excitation light and the secondary emission, a specific color impression of the emitted light can thus be produced in each case. In particular, white light can thus also be generated. A high degree of doping, i.e. a high density of conversion centers in the optoceramics, leads to a shortening of the absorption length compared to the scattering length. A high degree of doping leads to a shortening of the absorption length. This can be adjusted, for example, via the cerium content and set in a certain relation to the scattering length. If the absorption length is significantly less than the scattering length, it is mainly the converted light that is emitted. However, if the absorption length is greater than the scattering length, excitation light is mainly reflected. If the excitation light is blue and the secondary light is yellow, for example, a regime can be set in which the emitted converted light and the remitted excitation light produce a white color impression by mixing.

The converter according to the invention can be used in projectors, for example in projectors with a DLP, 3-chip DLP or LCD technology. Another possible use is the Use in lamps with high luminance, for example in stage lights or car lights. It can also be used in lamps with high luminance and high spectral density, such as those used in spectroscopy, for example.

Figure list

• 1 den schematischen Aufbau eines Konverters in Remission als ein erstes Ausführungsbeispiel.
• 2 den schematischen Aufbau einer Weiterbildung des ersten Ausführungsbeispiels mit einem dichroitischen Filter
• 3 schematisch die Verwendung der Optokeramik in einem Konverter in Transmission als ein drittes Ausführungsbeispiel.
• 4 schematisch einen Konverter in Transmission mit verbesserter Fassung als ein viertes Ausführungsbeispiel.
• 5 den schematischen Aufbau eines dynamischen, d.h. rotierenden Konverters in Remission, bei dem die Optokeramik als Ring ausgebildet ist.
• 6 den schematischen Aufbau eines dynamischen, d.h. rotierenden Konverters in Remission, bei dem die Optokeramik 1 als Ring ausgebildet ist.
• 7 den schematischen Aufbau eines dynamischen Konverters, der ,in Transmission arbeitet.
• 8: ein Diagramm zur Abhängigkeit von Quanteneffizienz und Remission.
• 9: ein Überlagerungsdiagramm zur Abhängigkeit von Remission und Quanteneffizient von der Sintertemperatur einer Optokeramik der Zusammensetzung Lu₃(Ga,Al)₅O₁₂-Ce
• 10: ein Überlagerungsdiagramm zur Abhängigkeit von Remission und Quanteneffizient von der Sintertemperatur einer Optokeramik der Zusammensetzung Y₃Al₅O₁₂-Ce
• 11: Diagramm zur Abhängigkeit der Remission vom Cer-Gehalt
• 12: ein Konverter mit Einstellung eines definierten Anteils von Anregungslicht zur Erzeugung eines Weißfeld-nahen Punktes im Farbort-Diagramm.

The invention is explained in more detail below on the basis of exemplary embodiments and with reference to the accompanying drawings.
Show it:

• 1 the schematic structure of a converter in remission as a first embodiment.
• 2 the schematic structure of a development of the first embodiment with a dichroic filter
• 3 schematically the use of the optoceramic in a converter in transmission as a third embodiment.
• 4th schematically a converter in transmission with an improved version as a fourth embodiment.
• 5 the schematic structure of a dynamic, ie rotating, converter in remission, in which the optoceramic is designed as a ring.
• 6th the schematic structure of a dynamic, ie rotating, converter in remission, in which the optoceramics 1 is designed as a ring.
• 7th the schematic structure of a dynamic converter that works in transmission.
• 8th : a diagram of the dependence of quantum efficiency and remission.
• 9 : an overlay diagram of the dependence of remission and quantum efficiency on the sintering temperature of an optoceramics with the composition Lu ₃ (Ga, Al) ₅ O ₁₂ -Ce
• 10 : an overlay diagram of the dependence of remission and quantum efficiency on the sintering temperature of an optoceramic with the composition Y ₃ Al ₅ O ₁₂ -Ce
• 11 : Diagram showing the dependence of the remission on the cerium content
• 12th : a converter with setting of a defined proportion of excitation light to generate a point close to the white field in the chromaticity diagram.

The exemplary embodiments of the invention are described below with reference to the figures.

1 shows the side view of a schematic structure of a converter operated in remission as a first exemplary embodiment.

The optical ceramic according to the invention 1 is by means of an adhesive layer 2 on a mirror 3 fixed. The adhesive layer 2 has a thickness d _glue of 10 μm. The mirror 3 reflects the excitation light 4th into the optoceramics 1 and thus increases the light yield in the form of converted, long-wave light 5 .

wobei für $${\text{T}}^{\text{max}}{}_{\text{Konv}}={\text{T}}_{\text{RT}}+\text{Q/A}*\text{d/}\mathrm{\lambda }$$

und den thermischen Widerstand R^th = d/(Aλ) gilt. Es gelten für die Wärmeleitfähigkeiten λ des ersten Ausführungsbeispiels
Wärmeleitfähigkeit Optokeramik λ_oc = 10 W/mK
Wärmeleitfähigkeit Kleber λ_Kleb = 0, 3 W/mK
Der thermische Widerstand des Konverters ergibt sich aus den absoluten thermischen Widerständen Rth des Konvertermaterials und des verwendeten Klebers.The converter area A is 4 mm ² , the thickness of the converter d _conv is 200 μm. The maximum pump output can be estimated: $${\text{P}}^{\text{Max}}{}_{\text{opt}}~\mathrm{4th}\left({\text{T}}^{\text{Max}}{}_{\text{Conv}}-{\text{T}}_{\text{RT}}\right){\text{/ R}}_{\text{th}}$$

where for $${\text{T}}^{\text{Max}}{}_{\text{Conv}}={\text{T}}_{\text{RT}}+\text{Q / A}*\text{d /}\mathrm{\lambda }$$

and the thermal resistance R ^th = d / (Aλ) applies. It applies to the thermal conductivities λ of the first embodiment
Thermal conductivity of optoceramics λ _oc = 10 W / mK
Thermal conductivity glue λ _glue = 0.3 W / mK
The thermal resistance of the converter results from the absolute thermal resistance Rth of the converter material and the adhesive used.

With the thermal resistances of optoceramics 1 R ^th _oc = 5 K / W and the adhesive layer 2 R ^th _{Adhesive = 8.3} K / W, this results in a thermal resistance R ^th Conv of 13.3 K / W for the converter. The adhesive layer 2 has a higher thermal resistance than the opto-ceramic 1 and thus decisively determines the thermal resistance, ie in this case its lower limit.
In the case of a damage threshold of the optoceramics 1 T ^max _oc = 250 ° C. therefore maximum pump powers P ^max _opt of 68 W. Only the adhesive layer has a limiting effect.

With a damage threshold of 100 ° C for the adhesive, the maximum optical pump power of P ^max _opt = 36 W.

This surprisingly high pump power enables, for example, with an irradiation with 10W on 4mm ² luminance of 200 cd / mm ² and a luminous flux of 600 1m.

In comparison to this, with the converters known in the prior art based on a phosphor in silicon, phosphor in silicon (PIS), maximum optical pump powers P ^max _opt of approx. 3 W can be achieved. This is due in particular to the high thermal resistance R ^th _PIS of approx. 100 K / W as well as the low damage threshold of the converter material.

2 shows the schematic structure of the second embodiment. This is a variant of the first exemplary embodiment, in which additionally on the optoceramics 1 an anti-reflective coating 6th was applied. This will reduce the scattering of the excitation beam 4th through the surface of the optoceramic 1 reduced. This reduces the size of the emission spot.

3 shows the structure of the third embodiment, a converter with rear excitation, that is, with transmissive excitation. The excitation beam 4th meets on the suggestion side 11 on the optoceramics 1 . On the issue side 12th comes the secondary light 5 out. The thickness of the optoceramic 1 is 200 microns. This ensures a sufficiently high transmission with good quantum efficiency. The optoceramics 1 is only laterally, ie to the left and right of the light spot of the excitation light, of the metallic socket 70 fixed. The predominant part is optoceramics 1 thus floats freely between the sockets. This design is only made possible by the fact that the optoceramics 1 is self-supporting. In contrast to this, systems known from the prior art, such as PIS, require substrates as carrier materials, so that excitation from the rear is not possible. The version 70 is designed as a heat sink and has a diameter of 2 mm. The optoceramic is used to reduce the size of the emission spot 1 on the suggestion page 11 with an edge filter 91 coated. The issue side 12th is in turn coated with a broadband AR coating.

The in 4th The structure shown schematically represents a further development of the third exemplary embodiment. Here is the optoceramics 1 edged so that the socket 71 apart from the area on which the light spot of the excitation light 4th falls, a large part of the bottom of the optoceramic 1 covered. The version 71 is metallic and reflects the excitation light 4th in optoceramics 1 . As a result, the secondary light is reflected in the optoceramic and the light confinement is increased. An additional coating of the opto-ceramic can be used here 1 on the suggestion page 11 be waived.

Assuming the same material data as in the first exemplary embodiment, the result is an effective thermal resistance R ^th _eff of 55 K / W. This makes optical pump powers P ^max _opt of up to 16 W possible.

The deviation from the optical pump powers of the first exemplary embodiment is due to the structure.

Depending on the operating configuration, the performance here still depends, for example, on geometry factors. This means that the maximum pump power in transmission is lower than in remission.

The following table shows an overview of the data of the converter material according to the invention that are relevant for the thermal FOM of a static converter, as well as a comparison of converter materials based on silicone or glass / glass ceramic.

The product of the maximum permissible temperature and thermal conductivity was selected as the thermal FOM for a statically operated converter.

Converters according to the invention have an FOM _stat of up to 7322 W / m, while analog converters with fluorescent material in silicone, on the other hand, only have an FOM of 95 W / m.

In the last column, the FOM was supplemented by the heat storage number. The heat storage number is the product of heat capacity and density. The expanded FOM, FOM _dyn describes the behavior of a converter on a rotating wheel and thus for a dynamic converter.

The optoceramics OC1 and OC2 according to the invention show extremely high FOMs.

The two optoceramics OC1 and OC2 differ in their doping. Optoceramics OC1 contains YAG (yttrium-aluminum-garnet), optoceramics OC2 Mg ₃ Al ₈ [SiO] ₃ .

The differences in the FOM of the two optoceramics are, however, due in particular to the different densities.

The materials listed in the table can be divided into three groups with regard to FOM. The low FOMs of converters based on silicone matrices can be attributed in particular to the low thermal conductivity.

Materials based on glass or glass ceramic show FOMs which are significantly higher than those of silicone matrices, i.e. organic systems. However, the FOM of the optical ceramics according to the invention are more than 5 times as high as those of converters based on glass ceramics.

In particular, the optoceramics advantageously have outstandingly high thermal conductivities λ. Table 1: Overview of the FOM-relevant data material Cp [J / K * g] Cp * p [J / cm ³ K] λ [W / mK] TQE / 8 0 [° C] T _abs [° C] Min (TQE80 / T _abs ) FOM _stat [W / m] FOM _dyn [J ² / cm ⁴ Sk] OC 1 0.6 2.76 14th 250 1700 523 7322 202 OC 2 0.6 2.28 10 250 1700 523 5230 119 silicone 1.4 1.7 0.2 250 200 473 95 1.6 Glass 1 2.5 0.9 300 500 573 443 11.1 Glass ceramic 1 2.5 1.5 250 900 523 859 22nd

This in 5 The fifth exemplary embodiment shown shows the schematic cross section of a dynamic converter which is operated in remission. The optoceramics 1 is designed as a circular disc by means of the adhesive layer 2 on the carrier 3 upset. The surface of the optoceramics 1 is with an edge filter 9 coated. The carrier 3 is centered with a hub 8th connected. The excitation is locally limited at one point on the converter. With the help of the hub 8th becomes the carrier 3 with the optoceramics 1 turned. Thus, a local specific local area of the optoceramics becomes 1 only for a short period with the excitation light 4th irradiated. The local irradiation time can be determined via the rotational frequency of the hub 8th be managed. Due to the short local irradiation time, high excitation powers of well over 25 W can be used.

The in 6th The exemplary embodiment shown schematically is the optoceramics 1 designed as a ring and with the help of the adhesive layer 2 on the circular support 3 applied. The use of a ring-shaped optoceramic 1 allows a lower cost of materials, but without affecting the optical properties of the converter. This is possible because in this embodiment only the areas are left out that are not exposed to the excitation beam anyway 4th are recorded.

7th shows the schematic representation of a dynamic, ie rotating, converter in transmission. In this embodiment the carrier is circular 13th designed as a reflective version, which the ring-shaped optoceramics 1 fixed. The carrier 3 covers only so much of the underside of the optoceramic 1 how is necessary to fix them. Most of the underside of the optoceramic is not taken by the carrier 3 covered and can thus be used for the conversion. The optoceramics 1 is also here on the excitation side, ie its underside, with an AR coating 10 and on its top with an edge filter 91 Mistake.

8th shows the relationship between quantum efficiency and remission. The relationship between scattering and remission can, however, advantageously be used to quantify the scattering properties of a converter. For this purpose, the remission is measured at a wavelength above the excitation wavelength. In this case, the remission of a sample of the converter material with a thickness of 1 mm was measured at a wavelength of 600 nm. A spectrometer with an integrating sphere was measured as the spectrometer. In the following, the remission R _emission measured according to this measurement specification is representative of an optical measurement of the scattering properties. The remission was determined using a sample with a thickness of 1 mm at a wavelength of 600 nm. A strongly scattering material has a high remission.

As expected, the quantum efficiency would decrease with strongly scattering samples. The expected behavior is indicated in the diagram by a straight line.

Most surprisingly, however, a regime 14th can be determined whose samples show a high remission, but without significantly influencing the quantum efficiency.

Optoceramics have thus been created which have a remission at 600 nm of 0.7 to 0.95 and whose quantum efficiency is above 0.85.

This extraordinary property of the optoceramics according to the invention is the result of a special composition of the starting mixture as well as the manufacturing conditions. Surprisingly, it has been shown that the scattering of the optoceramics can be adjusted via the choice of the sintering temperature. This is explained below using the in 9 and 10 examples shown. 9 and 10 show the dependence of remission, quantum efficiency and the product of remission and quantum efficiency of two cerium-doped optoceramics of different composition.

9 shows an overlay diagram of an optical ceramic with the composition LU ₃ (Ga, Al) ₅ O ₁₂ -Ce, the optical ceramic in FIG 10 has the composition Y ₃ Al ₅ O ₁₂ -Ce.

In both cases, the remission depends on the sintering temperature, while this is only weakly pronounced in the case of quantum efficiency. This is especially true in 9 clear.

An increase in the sintering temperature by 100 ° C halves the remission, while the quantum efficiency remains almost constant.

As in 10 shown, this effect is far less pronounced in the case of the second optoceramic.

The extent of the effect can in particular depend on the composition of the starting material.
The relationship between the two quantities depends on the density of the conversion centers, ie on the degree of doping.

11 shows the dependency between the absorption efficiency and remission or scattering of optoceramics according to the invention with different degrees of doping of Ce ₂ O ₃ .
The absorption efficiency describes the proportion of the absorbed excitation light in relation to the irradiated excitation light. It is calculated according to 1-R_Excitation from the remission of the blue excitation light. The remission of the blue excitation light was measured on 1 mm thick samples in a quantum efficiency measuring station.

Optoceramics with high levels of doping (0.2 wt% Ce ₂ O ₃ ) show a strong dependency on A absorption efficiency and remission. The absorption efficiency decreases rapidly, especially at high reflectance values from 0.8.

It is shown that the absorption efficiency for blue light or the blue remission R_Excitation can be set within wide limits by setting the scattering or yellow remission R_Emission.

By setting the scattering largely independently of the quantum efficiency, on the one hand good light confinement and thus high luminance levels can be achieved.

On the other hand, it is possible to adjust the scattering in such a way that the mixture between remitted excitation radiation R_Excitation and secondary emission leads to a specific color impression that lies on the conversion line in the chromaticity diagram. The conversion line is the connecting line between the color point of the excitation light and the color point of the emission spectrum

Based on 12th Another exemplary embodiment is described which enables a point close to the white field to be set in the color spectrum diagram. The converter is for the return operation 1 with a mirror 31 Mistake. In order to get close to the white field on the conversion line in the color spectrum diagram, the converter 1 selected with regard to its scattering properties so that 20% of the blue excitation light is remitted and 80% is absorbed. Most of the absorbed part of the excitation light is converted into yellow light and either directly or after reflection on the mirror 31 as a scattering lobe 51 emitted.
The blue remitted light is made up of a Fresnel reflex 40 and a scattering lobe 41 together. This scatter lobe 41 has a Lambertian radiation characteristic.
The point near the white field is now shifted by adjusting the converter thickness. Is this so low that excitation light shines on the mirror 31 is reflected and emerges again at the surface, a second scattering lobe is created 42 . This second scattering lobe 42 has - depending on the converter thickness and scattering - a more or less directional radiation characteristic. By superimposing the scattering lobes 40 , 41 , 42 of the excitation light and the scattering lobe 51 of the converted light there is an angle dependency of the color impression.
The angle dependency can be reduced by roughening the converter surface.

The fine adjustment to reach the point close to the white field can alternatively be done by applying a thin scattering layer on the excitation side of the converter 1 respectively. The scattering layer can consist of TiO ₂ or undoped, optoceramic material, for example. In both cases, the blue component is increased compared to the yellow component of the emitted light. In order to get into the white field of the chromaticity diagram, the yellow light can be reduced in green parts by filtering. This can be achieved, for example, with a dichroic mirror that reflects the blue light, but allows the green light to pass through so that it does not emerge on the useful side of the converter.

The converter materials according to the invention show tailor-made thermal, thermo-optical and optical properties.

Their synergetic interaction enables very high luminance levels of more than 100 cd / mm ² .

Claims (15)

Converter arrangement for generating colored or white useful light of high luminance for projectors, stage headlights, car headlights or lamps with high luminance and high spectral density, whereby the most complete possible decoupling of the converted light is to be achieved while at the same time spatially small emission spot, comprising: - A converter body (1) with an excitation side and a side facing away, containing an optoceramic with YAG ceramic or LuAG ceramic with embedded grain structure for purposes of strong light scattering, - An excitation light source with a light beam cross-section which determines the spatially small emission spot to be reached, the excitation light source being arranged to irradiate the converter body (1) with blue excitation light of high power density, which generates a blue light scattering spot and secondarily the emission spot that is larger than the light beam cross-section is the excitation light source, - The thickness of the converter body (1) between the excitation side and the opposite side is chosen to be sufficiently thin to minimize the spread of the light scattering spot on the one hand and to effect a sufficient conversion of the blue excitation light with regard to the color of the useful light on the other Converter arrangement according to Claim 1 , whereby the light scattering ability of the converter material is chosen so that with a 1mm thick converter body long-wave light of 600nm wavelength with a remission factor R _emission > 0.6 is remitted. Converter arrangement according to Claim 1 or 2 , whereby converter material with a quantum efficiency QE> 0.80 is used. Converter arrangement according to one of the Claims 1 to 3 , whereby converter material with an optical converter figure of merit QE · R _emission > 0.6 with simultaneous quantum efficiency greater than 0.80 is used. Converter arrangement according to one of the Claims 1 to 4th , whereby converter material with a thermal figure of merit (FOM _{therm, stat} )> 1000 (W / m) is used, which is calculated from the product of the maximum permissible temperature in Kelvin and the thermal conductivity of the converter material. Converter arrangement according to one of the Claims 1 to 5 , in which the thermal conductivity of the converter material is at least 5 W / m * K, preferably at least 10 W / m * K and particularly preferably at least 12 W / m * K. Converter arrangement according to one of the Claims 1 to 6th , at which a luminance of >> 100 cd / mm ² prevails in the useful light luminous spot in static operation. Converter arrangement according to one of the Claims 1 to 7th , in which the converter body (1) is self-supporting. Converter arrangement according to one of the Claims 1 to 8th , in which the converter body (1) is coated on the excitation side with a dichroic filter (6). Converter arrangement according to one of the Claims 1 to 9 , in which the converter body (1) is provided on the emission side with a broadband anti-reflective coating and / or an anti-reflective structure. Converter arrangement according to one of the Claims 1 to 10 , in which the converter material has a doping with cerium in the range of 0.01 and 2% and particularly preferably 0.1 and 0.5%. Converter arrangement according to one of the Claims 1 to 11 , in which, due to light scattering, the remission factor of the blue excitation light is just so high that a remission of the blue excitation light also takes place, so that the mixture of the excitation light and the converted light creates a white color impression in the viewer. Converter arrangement according to one of the Claims 1 to 12th , whereby the converter body (1) is designed with such scattering properties as to remit between 10% and 30% of the excitation light, and with a fine adjustment of the emission of the excitation light with a view to reaching an area close to white light by reducing the thickness of the converter body (1 ) he follows. Converter arrangement according to Claim 13 , wherein the excitation side of the converter body (1) is roughened. Converter arrangement according to Claim 11 , in which the excitation side (11) of the converter form the back and the emission side (12) form the front and the thickness of the converter body (1) is chosen so that a high luminance spot with the desired color impression is created for the viewer.

Images